The invention relates to an extrusion head having a perforated plate of a granulating system. The extrusion head can have a head part which constitutes the transition to an extrusion device, and a perforated plate with a central inflow cone, nozzle channels, and perforated dies of a perforated plate for the extrusion of granulation strands. The perforated plate with a central inflow cone, nozzle channels, and perforated dies can be detachably fastened to the head part. The head part of the extrusion head can have at least one central melt channel into which the inflow cone of the perforated plate projects and distributes the melt flow among nozzle channels which can be arranged in the shape of at least one ring, and among the adjoining perforated dies of the perforated plate.
Known to persons having ordinary skill in the art is an underwater granulator that has an extrusion head with a head part, a central melt channel, and with a perforated plate of complex construction, as is shown in FIG. 6 attached hereto for the purpose of clarification. The one-piece perforated plate has an inflow cone, nozzle channels, perforated dies, and is subjected to relatively high wear depending on operating conditions since circulating granulator blades sweep in a rotating manner along an outer contact surface with openings of the perforated dies in order to sever granulate strands emerging from the openings into granules. The granules are then discharged from the underwater granulator in a cooling water flow in the direction of the arrow A.
Once such a complex perforated plate reaches the predefined wear limit at the outer contact surface, it along with its integrated inflow cone, integrated nozzle channels, and integrated perforated dies, must be replaced by new perforated plate or recycled, both of which are cost-intensive. Moreover, such a prior art extrusion head experiences accelerated aging due to corrosive attack on screw heads by the cooling water flow. The screw heads of screwed connections, which connect the complex perforated plate to the head part of the extrusion head are unprotected and exposed to the cooling water flow.
One object of the present invention is to delay the aging of extrusion heads and to reduce the maintenance costs, assembly costs, replacement costs, and wear costs of the perforated plates of the extrusion heads, and to reduce the corrosion of component parts.
This object is attained by the present invention.
The present embodiments are detailed below with reference to the listed Figures.